1. Field of the Invention
The present invention relates, in general, to a system and method for calibrating an offset of a position sensor of a motor in an algebraic solution, instead of a geometrical solution as is done conventionally.
2. Description of the Related Art
Recently, with the increased need for eco-friendly vehicles, drive systems within these vehicle are being increasingly replaced with an electronic motor. Such eco-friendly vehicles include hybrid vehicles, electric vehicles, fuel cell vehicles, etc. which all use a motor as a drive source.
Such motors generally use a position sensor called a resolver that is installed on a shaft of the motor. The resolver may be thought of as a transformer in which a certain magnitude and frequency of voltage is applied to an input thereof and a transformation ratio varies depending upon the position of a rotor. Also, a signal that is amplitude modulated by sinusoidal and cosine functions with respect to the position of the rotor is output to tow outputs thereof. An RDC calculates the position of the resolver when the output is input. This is also a reason why the offset between the rotor positions of the motor rotor and resolver rotor needs to be calibrated.
In dynamic models (DYNAMO) for a motor, because of the existence of a torque sensor, it is possible to correctly set the offset of a resolver by applying −d-axis current to the motor to find the location in the motor where there is no torque. However, when motors have to be replaced in garages after having been mass produced, the garages generally do not have DYNAMO equipment and therefore no torque sensor as well. Accordingly, the appropriate angle must be calibrated using geometric software.
To this end, in the case of hybrid vehicles, a revolution speed is somewhat controlled by an engine that is directly connected with a motor. In the motor, however, when 0 current control is applied, the voltage that is generated corresponds to back electromotive force, so that when the offset calibration is corrected, only q-axis voltage occurs. Thus, when the calibration is not correct, d-axis voltage is also generated so that the offset can be calibrated using the magnitude of d-axis voltage.
This is a conventional offset-calibration method. While this method has no problem being used when the d-axis and q-axis are kept perpendicular, when there are any manufacturing defects, in the coordinates of an observed system as shown in FIG. 2, the d-axis and q-axis are not perpendicular, so that such a method is not applicable.
In the related art, such an offset may be calibrated using the following methods. A conventional offset calibration method will now be described with reference to FIGS. 1 and 2. In the conventional art, typically one or more hybrid control units (HCU) 101 is configured to control an engine 102 and motor 103 and an motor control unit (MCU) that is configured to control the motor current. In particular, in the convention method current is only applied to −d-axis in order to prevent generation torque, and thus when torque is generated, Δθ is calculated and reflected thereto, so that the offset of a resolver is calibrated by the following equations.
            v              α        ⁢                                  ⁢        β              =                            ⅇ                                    -              j                        ⁢                                                  ⁢            Δ            ⁢                                                  ⁢            θ                          ⁢                  v          dq                    =                        j          ⁢                                          ⁢                                    v              q                        ⁡                          (                                                cos                  ⁢                                                                          ⁢                  Δ                  ⁢                                                                          ⁢                  θ                                -                                  jsin                  ⁢                                                                          ⁢                  Δ                  ⁢                                                                          ⁢                  θ                                            )                                      =                                            v              q                        ⁢            sin            ⁢                                                  ⁢            Δ            ⁢                                                  ⁢            θ                    +                      j            ⁢                                                  ⁢                          v              q                        ⁢            cos            ⁢                                                  ⁢            Δ            ⁢                                                  ⁢            θ                                          v      α        =                            v          q                ⁢        sin        ⁢                                  ⁢        Δ        ⁢                                  ⁢        θ        ⁢                                  ⁢                  v          β                    =                                    v            q                    ⁢          cos          ⁢                                          ⁢          Δ          ⁢                                          ⁢          θ          ⁢                                          ⁢                      Δ            ⁢                                                  ⁢            θ                          =                                                            tan                                  -                  1                                            ⁡                              (                                                      v                    α                                                        v                    β                                                  )                                      ⁢                                                  ⁢                          θ              updated                                =                      θ            -                          Δ              ⁢                                                          ⁢              θ                                          
However, since as previously described, a problem with such a method is that because of manufacturing errors, in the coordinates of an observed system, the d-axis and the q-axis are originally and potentially not perpendicular, even though AO is calculated and reflected thereto, so that the method essentially involves errors.
The description of the related art is merely for the purpose of understanding the background of the present invention, so it should not be construed to the person skilled in the art that the description of the present invention is admitted as pertaining to the related art.